1. Field of the Invention.
This invention relates generally to an identification friend or foe (IFF) system and particularly to an IFF system that may be used by a launched weapon to distinguish friend from foe and divert to avoid damaging or destroying friendly targets. Still more particularly, this invention is directed to a passive system in which friendly targets are equipped with light sources that emit encrypted ultraviolet (UV) signals that may be detected by a missile or torpedo.
2. Description of the Prior Art.
Current technology for distinguishing friend from foe places the decision on the weapons launcher prior to launch of a missile, torpedo or other ordnance. Prior IFF systems use radio frequencies that are exploitable over long distances because they are designed to transfer information over long distances. A problem with prior IFF systems is that once launched, a weapon is unable to recognize a target as friendly and divert. This problem arises because weapon ranges exceed the ranges at which IFF is possible and because weapons such as torpedoes are designed to find targets but not to discriminate between friend and foe.
An object of the invention is to provide a system that disarms a weapon after a selected target is identified as being friendly.
Still another object of the invention is to provide a system that causes a weapon to make a collision avoidance maneuver after identifying a selected target as being friendly.
Accordingly an identification friend or foe system according to the invention for use by a weapon to determine whether a target that has been selected is a friendly target comprises a signal source attached to the target and arranged to radiate encrypted signals. A detection system attached to the weapon includes a receiver arranged to receive the encrypted signals when the weapon is within a predetermined range from the target. Signal processing apparatus is connected to the receiver and arranged to determine whether the encrypted signals identify the target as being friendly.
The identification friend or foe system of claim 1 wherein the receiver comprises a photodetector that produces electrical signals in response to encrypted signals incident thereon and wherein the signal processing apparatus includes an amplifier connected to the photodetector and a central processing unit connected to the amplifier. The central processing unit is arranged to decrypt the encrypted signal and produce a disarm signal if the target is identified as being friendly.
The central processing unit preferably is also arranged to produce a signal that causes the weapon to perform a collision avoidance maneuver to avoid colliding with the target if the target is identified as being friendly.
The signal source preferably produces encrypted signals in the ultraviolet region of the electromagnetic spectrum.
The encrypted signals preferably have a wavelength that is attenuated in the atmosphere such that there is a predetermined maximum range from the target at which the encrypted signals are detectable by the photodetector.
The invention further includes a method for identifying friend or foe system for use by a weapon to determine whether a target that has been selected is a friendly target that comprising the steps of (a) attaching signal sources to friendly targets, (b) arranging the signal sources to radiate encrypted signals that identify the targets as being friendly, (c) attaching a detection system to the weapon, (d) receiving the encrypted signals with the detection system when the weapon is within a predetermined range from a selected target, (e) connecting signal processing apparatus detection system, and (f) arranging the signal processing apparatus to determine whether the encrypted signals identify the target as being friendly.
The method according to the invention preferably further includes the step of arranging the signal processing apparatus to produce a disarm signal that disarms the weapon if the target is identified as being friendly.
The method preferably also includes the step of arranging the signal processing apparatus to produce a signal that causes the weapon to perform a collision avoidance maneuver to avoid colliding with the target if the target is identified as being friendly.